Refactor code

[Kien Nguyen]

At the moment, Zun code still has many `ugly` codes: meaningless naming, unused vars, methods,...
So I think we need to improve it, refactor codes:
- Remove unused method, variable, class.
- Remove unnecessary methods, vars, etc.
- Optimize code.
- Rename variables, methods.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/481418

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/481563

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/481418
Committed: https://git.openstack.org/cgit/openstack/zun/commit/?id=c2ea4329fa2f7c546e8adb272cec272fbbe0ad1c
Submitter: Jenkins
Branch: master

commit c2ea4329fa2f7c546e8adb272cec272fbbe0ad1c
Author: Kien Nguyen <email address hidden>
Date: Fri Jul 7 11:51:57 2017 +0700

    Rename kw to kwargs

    Change-Id: I0530dd63f5960c9df1e791a419c5c43f19b689ec
    Partial-Bug: #1702587

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/482489

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/482787

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/482489
Committed: https://git.openstack.org/cgit/openstack/zun/commit/?id=56592105f9538c5961984d50df321a1f219381a0
Submitter: Jenkins
Branch: master

commit 56592105f9538c5961984d50df321a1f219381a0
Author: Kien Nguyen <email address hidden>
Date: Tue Jul 11 16:52:36 2017 +0700

    Refactor code

    - Fix pep8 error H903: [1]
    - Add method _update_task_state to reduce code lines.
    - Change single quotes to double quotes in docstring - PEP8 docstring
    convention [2].

    [1] http://paste.openstack.org/show/614990/
    [2] https://www.python.org/dev/peps/pep-0257/

    Partials-Bug: #1702587

    Change-Id: Idd125665a2a5f0a73337d36f0259a9f9107946ad

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/482787
Committed: https://git.openstack.org/cgit/openstack/zun/commit/?id=4fcb465879f904cb04da99a7f48cd71db486edbd
Submitter: Jenkins
Branch: master

commit 4fcb465879f904cb04da99a7f48cd71db486edbd
Author: Kien Nguyen <email address hidden>
Date: Wed Jul 12 10:41:02 2017 +0700

    Fix some errors and warnings

    - Dictionary contains duplicate keys.
    - Unexpected arguments.
    - Missed call to __init__ of super class.
    - Missing import i18n marker function in zun/api/controllers/v1/images.py.

    Change-Id: I75c3ce3049ff62ae08868fdcce680945783690fd
    Partials-Bug: #1702587

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/481563
Committed: https://git.openstack.org/cgit/openstack/zun/commit/?id=d7d1b6821f48a1a0fcc56e85496c9d0a0c73aedb
Submitter: Jenkins
Branch: master

commit d7d1b6821f48a1a0fcc56e85496c9d0a0c73aedb
Author: Kien Nguyen <email address hidden>
Date: Fri Jul 7 17:22:20 2017 +0700

    Refactor Glance Image driver

    - In update_image method, has tag arg or not, always return
      update_image_format. The called method, update_image_tags,
      doesn't do any works.
    - Add new method download_image_in_chunks like another methods.
      Init glanceclient in utils module.
    - Update testcases.

    Change-Id: I3a3e9ec38c39ae4abc12196d907b1f32096ad9b6
    Partial-Bug: #1702587